One of the concerns with an enriched food waste feedstock is the potential for pathogens like E. coli and Salmonella to proliferate and contaminate compost.

It is well known and established in composting operations that piles do not everywhere achieve sufficient temperatures to destroy these pathogens. Many pathogens survive composting temperatures. This is a major concern as the chances of pathogens ending up in the final product (compost) are improved as more and more food waste enters into the composting process.

Bokashi (Acidic anaerobic) fermenting results in the accumulation of numerous carboxylic acids including butyric, valproic and caproic acids, and these metabolites are highly lethal to pathogens. Fermenting is done by excluding oxygen. The pH shifts into the range 3.5 to 5.5 and the end points in fermenting are typically observed near pH 4.0.

Many tests with 3M petri film and laboratory cultures reveal coliforms including Salmonella do not survive in this fermenting environment and pathogens are rapidly destroyed. The process is so efficient that it is even used to destroy pathogens in pet waste.

Many reports in the literature confirm that pathogens are rapidly destroyed in a low pH environment in the presence of butyric and caproic acids.

Fukishi et. al showed that Salmonella spp are completely eliminated in less than 2 days in the presence of these acids when the pH is less than or equal to 5.5.

E. coli O157 does not do well with organic acids at low pH and with the addition of metabolites forming in the fermenting do not survive. Acids produced in bokashi fermenting all had profound killing impact on E. coli O157.

Even acid resistant rare forms fall off rapidly by the hour in acid media. Note that adding additional factors like anaerobic conditions, competing organisms (non-pathogens) multiplying rapidly in the acidic anaerobic environment, natural antibiotics secreted and expressed by fungi further have lethal impact on pathogens.

Zhao revealed even with highly selected adapted organisms, the killing is abundant and evident.

E. coli are killed very effectively by butyric acid (one of the metabolites observed as fermentation progresses in both pet waste and food waste). This is also very effective at killing Salmonella and other pathogens and is used in preventing pathogen growth on meat products.

Fecal contaminated drinking water containing E. coli O157 and other E. coli spp. was also shown to be efficiently treated with carboxylic acid metabolites found in the ferment.

It is the combination of acids (butyric, caproic, etc.) at low pH, lack of oxygen, natural antibiotics formed by fungi growing in the fermentation process, and likely nitrite derivatives formed in the reducing environment all contributing to effective elimination of pathogens that accounts for this efficient pathogen eliminating capacity. The real evidence is of course in the actual testing where none of the coliforms survive 24 hours in pet waste processing with fermenting.

These efficient pathogen killing mechanisms appeared active in an early pilot study in Armstrong BC in a study monitored by the BC Ministry of the Environment. In this study no pathogens were detected in the fermented end products and when that material was mixed with soil, the native coliforms in the soil were further reduced by 50%.

The presence of pathogenic microorganisms in municipal waste sludge may create a serious outbreak of water borne diseases if the sludge is used for agricultural purpose. An attempt to decrease the number of pathogenic microorganisms, Salmonella spp. using a simulated acid-phase anaerobic digester was tested in a laboratory-scale batch experiment. Reduction of Salmonella spp. was demonstrated in a mixture of sludge and organic acid, simulating an acid digester of a two-phase anaerobic digestion process. A high concentration of organic acid at a pH value of 5.5–6.0 prevents a decrease in Salmonella spp. concentration. Almost complete destruction of Salmonella spp. is observed within two days if the pH value is maintained below 5.5.

As you probably know, acidity works against botulism. The illness is related to toxins produced by these organisms and it is prevented in an acidic environment as the microbes responsible for the proliferation and formation of toxins don’t produce in acidic environment. Bokashi fermenting drops the pH to around 4.0 and it won’t work above pH 6.0. So you can see the risk is virtually nil. The other factor which may be interesting is the potential for bokashi fermenting to metabolize the toxins produced by the microbe. The toxin is a protein and that will be degraded and consumed by other microbes in the fermenting process as it is high value nutrient for competitors.

I hope that provides you with some answers.
Very Best Regards, Larry Green Bokashicycle LLC